3 ms·

Relevant: http://www.nrl.navy.mil/media/news-releases/2014/scale-model-wwii-craft-takes-flight-with-fuel-from-the-sea-concept http://www.nrl.navy.mil/media/news

by leoc 13y ago

Relevant: http://www.nrl.navy.mil/media/news-releases/2014/scale-model-wwii-craft-takes-flight-with-fuel-from-the-sea-concept http://www.nrl.navy.mil/media/news-releases/2014/scale-model... http://www.washingtontimes.com/news/2014/apr/10/game-changer-us-navy-can-now-turn-seawater-jet-fue/ http://www.washingtontimes.com/news/2014/apr/10/game-changer... . You can see why the technology would appeal to the US Navy, even if it's not quite price-competitive with other means of getting jet fuel: they're keen to untether their carrier groups from the supply chain as much as possible, which is partly why they have the convenient nuclear reactors already.

dredmorbius 13y ago
My read is that the "supply chains" arguments are largely incorrect. The scale of operations of the 100kgal/day site would vastly exceed the available onboard space available within any existing warship -- you'd need a floating platform of some sort dedicated to the task. Since the proposal presumes use of a carrier's own nuclear plant to supply power for the operation, the carrier would be physically tethered to the fuel synthesis platform. Carrier operations require operating at near flank (top) speed for takeoffs and landings. You couldn't fight and fuel at the same time. Even task-switching between modes would be at best cumbersome. The US NRL's own research materials propose a fixed-site pilot, perhaps powered by OTEC (ocean thermal energy conversion) as a renewable energy source (this provides constant 24/7 power based on sea temperature gradients from sites such as the Hawaiian Islands with proximate shallow and deep-water zones at large temperature differential). Similarly any electrical power source, most conceivably renewable solar or wind, or nuclear, could be used for fuel synthesis. My back-of-the-envelope calculations suggest that supplying the equivalent of present-day US petroleum consumption would be plausible. It would require a few thousand km^2 of solar capacity, a roughly 10m tall by 4.5m square processing plant, and capital of roughly $8 trillion (based on USNRL's estimates) for synthesis and likely 1-2x that for the solar capacity. In either case, you'd still have tankers and tenders transporting fuel, what you'd eliminate is the specific reliance on routes from existing petroleum extraction and refining sites. Overall efficiency should be vastly better than the levels discussed here. Limiting point seems to be hydrogen electrolysis, which is 60% efficient (in terms of hydrogen energy potential) based on existing operational data. The Fischer-Tropsch reaction is pretty low in energy demand, or net positive. There are _vast_ volumes of seawater which would have to be processed, and pumping of that could be a significant energy cost (or perhaps tidal flows and some clever one-way-flow solid-state valves could be used to accomplish this: http://makezine.com/2012/01/05/the-tesla-valve-one-way-flow-with-no-moving-parts/ http://makezine.com/2012/01/05/the-tesla-valve-one-way-flow-...). It's not clear to me what the actual efficiency of the USNRL's method would be, though it seems clear that 60% net energy recovery is a theoretical maximum. I'd suspect 20-50% might be reasonably attained -- and that's far, far higher than the 1.7% claimed by the article referenced by this HN post.
- leoc 13y ago
  > The scale of operations of the 100kgal/day site would vastly exceed the available onboard space available within any existing warship -- you'd need a floating platform of some sort dedicated to the task. How do they compare to the space available inside and on top of the latest post-Panamax container ships? Even having a handful of ships like that (with their own nuclear reactors) trailing after the carrier to supply the requirement might be somewhat viable.

by leoc 13y ago

dredmorbius 13y ago

My read is that the "supply chains" arguments are largely incorrect. The scale of operations of the 100kgal/day site would vastly exceed the available onboard space available within any existing warship -- you'd need a floating platform of some sort dedicated to the task. Since the proposal presumes use of a carrier's own nuclear plant to supply power for the operation, the carrier would be physically tethered to the fuel synthesis platform. Carrier operations require operating at near flank (top) speed for takeoffs and landings. You couldn't fight and fuel at the same time. Even task-switching between modes would be at best cumbersome. The US NRL's own research materials propose a fixed-site pilot, perhaps powered by OTEC (ocean thermal energy conversion) as a renewable energy source (this provides constant 24/7 power based on sea temperature gradients from sites such as the Hawaiian Islands with proximate shallow and deep-water zones at large temperature differential). Similarly any electrical power source, most conceivably renewable solar or wind, or nuclear, could be used for fuel synthesis. My back-of-the-envelope calculations suggest that supplying the equivalent of present-day US petroleum consumption would be plausible. It would require a few thousand km^2 of solar capacity, a roughly 10m tall by 4.5m square processing plant, and capital of roughly $8 trillion (based on USNRL's estimates) for synthesis and likely 1-2x that for the solar capacity. In either case, you'd still have tankers and tenders transporting fuel, what you'd eliminate is the specific reliance on routes from existing petroleum extraction and refining sites. Overall efficiency should be vastly better than the levels discussed here. Limiting point seems to be hydrogen electrolysis, which is 60% efficient (in terms of hydrogen energy potential) based on existing operational data. The Fischer-Tropsch reaction is pretty low in energy demand, or net positive. There are _vast_ volumes of seawater which would have to be processed, and pumping of that could be a significant energy cost (or perhaps tidal flows and some clever one-way-flow solid-state valves could be used to accomplish this: http://makezine.com/2012/01/05/the-tesla-valve-one-way-flow-with-no-moving-parts/ http://makezine.com/2012/01/05/the-tesla-valve-one-way-flow-...). It's not clear to me what the actual efficiency of the USNRL's method would be, though it seems clear that 60% net energy recovery is a theoretical maximum. I'd suspect 20-50% might be reasonably attained -- and that's far, far higher than the 1.7% claimed by the article referenced by this HN post.

leoc 13y ago
> The scale of operations of the 100kgal/day site would vastly exceed the available onboard space available within any existing warship -- you'd need a floating platform of some sort dedicated to the task. How do they compare to the space available inside and on top of the latest post-Panamax container ships? Even having a handful of ships like that (with their own nuclear reactors) trailing after the carrier to supply the requirement might be somewhat viable.